Currently, there are two methods for attaching metallic shields to modules or printed circuit boards, namely using conductive epoxy or solder paste. Each of these current methods has several detriments. In the case of conductive epoxy, the conductive epoxy is dispensed on a shield track and the shield is placed over the conductive epoxy. In a cost sensitive manufacturing environment, the cost of conductive epoxy is one primary issue. Another issue is the dispensing and curing process. These two processes require dedicated equipment and increased cycle time. Finally, the reliability of the conductive epoxy bond is also an concern. Conductive epoxy could change its electrical characteristics over time due to oxidation. Additionally, conductive epoxy can fail to provide sufficient adhesion to hold a shield in place for some applications and would likely cause the shield to fall off the module during a drop.
The alternative current method involves dispensing of solder paste on a shield track and the placement of the shield over wet paste. Such method imposes clearance requirements between the shield track and adjacent components to avoid solder shorts. As a result, the module size is unnecessarily increased. As with the conductive epoxy, the dispensing process requires dedicated equipment. Another issue with current solder dispensing processes is that the volume of the solder paste might not be sufficient to compensate for shield non-coplanarity.